Electric flatiron



Dec. 17, 1935.` M. H. GRAHAM ELECTRIC FLATIRN Filed June l5, 1934 ibmmm"` 172/ (zz fg 29 |||||||Ill`l /NvE/voz Maur/ce H. Gra/vam By Z/sryogsys Patented Dec.` 17, 1935 4UNITED STATES PATENT OFFICE ELECTRICFLATIBON Maurice H. Graham, St. Louis Park, Minn.

Application June 15, 1934, Serial No. 730,745

' 'l Claims. (Cl. 21S-25) My present invention relates to electricallyheated ilatirons and, generally stated, the invention consists of thenovel devices, combinations of devices and arrangement of partshereinafter 5 described and dened in the claims. The accurate regulationof heat in an'electrically heated fiatiron involves problems that arepeculiar to flatiron structures. The sole plate of the fiatiron, in use,will be subjected to various different heat-absorbing conditions,sometimes to delicate materials such as laces, chiffons and the like,which absorb heat very slowly, and sometimes to damp blankets andthelike, which absorb heat very rapidly. vIn practice and in accordancewith underwriters rules and regulations, one thousand watts is about thelimit which can be supplied to an electrical iiatiron or to any othercurrent-utilizing device over the ordinary wires of a houseinstallation.

Experience has shown that cast iron is the best metal for use in thesole plate of an electrically heated ilatiron. By experiment I havefound that for the greatest accuracy of heat control, the switchactuator should-be incorporated in the sole plate and should be of ametal that has a lower co-emcient of expansion and a slower rate'of heatexchange than the cast iron sole plate. I have further found that theemciency of the iron kwill be increased by incorporating the electricheating element also in the sole plate of the flatiron. The problem hasbeen yto find a metal for use as a switch actuator which will not onlyhave a lower co eilicient of expansion than cast iron, but will maintaina constant or even rate of expansion and contraction at the hightemperatures at which flatirons should be maintained in use.

Cast iron has been found to be the best for the sole plate of afiatiron. I have obtained substantially perfect results by making theswitch actuator in the form of a metal alloy bar or rod closely embeddedin the groove or slot in the sole plate and made of a nickel-steelalloy, to wit: an alloy consisting of 42% nickel 45 and 58% steel. Theco-eilicient of expansion of cast iron is .059, and that of thenickel-steel alloy .026. When thus made, the sole plate will have morevthan twice the expansion of the nickel-steel actuator bar. Moreover,the cast iron of the sole plate will absorb and radiate heat faster thanthe nickel-steel actuator bar, which action,`together with the fact thatthe actuator is embedded in the sole plate, give an ideal action thatwill hereinafter more fully 05 appear.

The proportions of nickel and steel in the above alloy are of greatimportance. A nickelsteel alloy consisting of 36% nickel and 64% steelis a metal known as invar metal." This invar metal, as is well known,expands and con- 5 tracts .very slightly intemperatures below 350degrees F., but at temperatures above 350 degrees F., it expands veryrapidly and unevenly so that it cannot be relied upon vfor accuratecontrol of a tiatiron, the temperature of which 10 should be around 500degrees F. At 500 de-v grees F., invar and cast iron have substantiallythe same co-eilicients of expansion. However, the 42% nickel-58% steelalloy has an even rate of expansion and contraction at all tem- 15peratures below 650 degrees F.

By experiment I have found that the nickel employed in the nickelrsteelalloy for the Switch actuator must not be less than 40% or more than5o%. The above 42%-58% nickel-steel zo alloy in the form of a bar is notfragile, has good strength and when embedded in the sole plate asstated, has been found to give a switch control that is almost perfectin-its accuracy. As a further important characteristic this nickel- 25steel alloy, in respect to cast iron, has a slower rate of heatexchange, that is, will not cool as rapidly or absorb heat as rapidly ascast iron.

The invention above outlined is illustrated in the accompanying drawing,wherein like chara0 acters indicate like parts throughout the severalviews.

Referring to the drawing:

Fig. i is a vertical section taken longitudinally through the major axisof an electric fiatiron 35. embodying my invention and illustrating avery desirable form thereof, some parts being shown in full;

Fig. 2 is a vertical section of the iron shown in Fig. 1, with thehandle, casing and certain 4e other parts removed, and some parts brokenaway; and

Fig. 3 is a fragmentary section taken on the line 3-3 of Fig. 2.

Referring to the drawing, the numeral 0 in- 45 dicates the sole plate ofa atiron which is of cast iron; and the numerals I0, I: and l2 indicate,respectively, the metal anchoring plate, the sheet metal shell or coverand the handle of the fiatiron. The said parts 0 and il are 50 shown asrigidly but detachably connected by screws i3 and the said elements I0,il and l2 are shown as rigidly but detachably connected by screws I4.For the highest eillciency, the electrical heating element, which isformed by 56 manifold wire coils I5, is embedded in the sole plate 9.Preferably, this embedding'of.. the coils I5 is accomplished ina-manner''disclosed' and claimed in my pending application, Serial No.

705,716, filed January 8, 1934, entitled "Elecare two manifold coils I5,the terminals of which are indicated at |5a and I5b. l

On the heel of the shell or cover IIV are the usual circuit leadterminals |8, to which theV socket ot an electric supply cable isadapted to be connected in the well-known manner.

A'Ihe supply circuit to they heating coils I5 includes an electricswitch which may take various forms but which, as illustrated in theseviews, Figs. l, 2 and 3, includes contact points I9 and 20 carried bythe up-turned prongs of a U-shaped spring switch 2|, the lower portionof which is anchored to the sole` plate 9 by ak short cross bar 22which, in turn, is rigidly butA detachably secured to thesole plate by`screws 23 `or the like. lThe contact point I9 is electrically connectedby a flexible metal ribbon 24` to one of the terminals |5a of theheating coil, and the other of said terminals |5a will,

by a wire, not shown, be connected to the other lead terminal I8, towit: the lead terminal to which the ribbon 25 is not connected. The saidlead terminals 8, of course, are insulated the `one from the other. Thecoil terminals |5b are electrically connected by a suitable conductorindicated in Fig. 2 at 26. Therearprong of the spring support 2| isYadapted to be variably set; and this, as` shown, is accomplishedby alpressure screw .21 that worksthrougha post 28 anchored to the heel orrear portion of the sole plate.

The switch actuator used in the iron illustrated in the drawing is shownas in the form of a at bar 29, made of the nickel-steel. alloy abovedescribed. This actuator barv is incorporated in the sole plate and isquite closely tted into a longitudinal groove 30 formed atthelongitudinal axis of the sole plate and extended at its rearportionintoa small well or y depression 3| in which the lower portion ofth switch 2| is shown as mounted.

At its rear end, switch actuator bar 29 is shown as provided with anupwardly and rearwardly projecting nger l32 that works through. a per'foration inthe front arm ofthe switch 2| and has a projecting lug thatexerts a forward pull y on the front arm of the switch 2| in theswitchcontact points I3 andj 2|| inengagement thereby'closing'.,lthfe'llliit through 'the electrical heating elexnei'ts oftheiiatiron, providingof course, that there isa supply of current to theterminals 8. Whenrheat is applied to the sole plate 5 from theelectrical heating coils, the sole plate will, with the materials aboveindicated, expand Y more than twice as fast as the actuator bar 29, andhence will exert a forward pullwon the bar 29; and at some certaintemperaturef'the bar 29, acting on the front arm ofthe switch 2|, willseparate the contacts I9 and 20, thereby automatically cutting off thesupply kof `current to the heating elements. f

The temperature at which the contacts I9 and 20 will be separated andthe ciment cut offvin the iron, may be varied by forward and rearwardadjustmentsv of the rear arm of the switch` 2 I, and which adjustmentis, as shown, accomplished by adjustments of the screw 21. 20 Assumethat the adjustment of the screw 21 is such that under the relativerapid expansion of the sole plate and the relativelyslower exf pansionof the bar 29, the latter, acting on. the switchv2|,`will separate thecontact points 25 |9 and 20 when the temperature of they sole platereaches 500 degrees F. 'I'he instant that the circuit is .thus broken bythe separation of thel contacts I9 and 20, the temperature ofthe sole'`plate of the atiron and Vall other Vparts 80 ofthe atiron, forthatmatter, willcommence 1 to recede, but the temperature of the soleplate will decrease more rapidly than that of the actuator` bar `29, andthere will be a lag in the lowering of temperature and hence` the con-$5 traction ofthe bar 29 inrecspecttothe lowering of temperature andVcontraction of the vsole plate., The bar `29 tends to maintain, for ashort interval, the length that is assumed at the' instant of breakingof thekcircuit, and while the 40 sole plate is -rnaking its initialcontraction. i This permits the initial contraction ofthe sole plate toagain close the switch, thereby again turning on the current as soon' asthe sole plate of thel atiron has beeny very slightly 45 reduced, towit: from 500 degrees F. to approximately 498.degrees F. l

When the current has been again turned on, and heat kapplied to theiron, there will be alag in the heat absorption and an expansion of the50 switch actuator bar 29 inrespect to the rapidity of theheat-absorption and expansion of the sole plate, so that when thetemperatureof the sole plate has been but slightly raised, to wit:`rback to the predetermined desired temperature `as- 55 sumed to'be'500degrees F.. the circuit will be again opened andthe currentv to thevheating element cut off. In actual experiments with atirons having Vaswitch actuator made of a material of a higher co-eillcientl ofexpansion 00` than the sole plate, it has been` found that the v lagwill then be in the sole platefand that this v lag worksagainst accuracyof control, so thaty there will be a drop or variation in temperature ofthe sole plate of approximatelyl degrees F., 05 depending somewhat onthe character ofthe work being ironed, but always of such materialvariation-as to destroyv accuracy of control.

The eiilciency of the scheme above described, requires the switchactuator to be embedded or 70 incorporated inthe sole plate so that itis subject to direct heat. exchange with the sole plate and islsubjected to the same temperatures; and the accuracy ofthe-control isimproved by having direct contact .between the switch actuator 16 andthe sole plate. Moreover, the emciency of the flatiron is furtherimproved by embedding the electrical heating element in the sole plateso that the three elements, to wit: the sole plate, the electricalheating element and the switch actuator, are incorporated substantiallyas a unit.

In the above description of the structure illustrated, the desiredtemperature is assumed to be 500 degrees F., but this predeterminedtcmperature may obviously be varied by varying the position of the rearcontact point I9 in respect to the contact point 20 through theadjustment of the screw 21 which acts on the rear arm of the springswitch member 2|.

What I claim is:

1. In an electric iron having a heating element and a supply circuit forsaid heating element including a switch; a sole plate, and a metallicswitch actuator associated with said sole plate and having asubstantially different coeiilcient of expansion tromthat of vthe soleplate, said actuator being a nickel-steel alloy in which the nickel isin a proportion oi from forty to mty percent o1 the total metal in thealloy, whereby said switch is operated by the di'erential expansion andcontraction oi said sole plate and actuator.

2. The structure dened in claim 1, in which said actuator is in the formof a bar, one end of which actuates said switch and the other end oi'which reacts against the sole plate at a point remote from said switch.

3. 'Ihe structure defined in' claim 1. in which said switch is at theheel end of said sole plate and said actuator is in the form of a barthat acts upon said switch at its rear end and the front end of whichreacts against the front toe end of said sole plate.

4. The structure defined in claim 1, in which said switch actuator andsaid heating element are incorporated in said sole plate.

5. In an electric iron having a heating element and a supply circuit forsaid heating element including a switch; a sole plate, and a metallicswitch actuator associated with said sole plate and having asubstantially different coemcient o! expansion i'rom that o! the sole 15plate, said actuator being a nickey steel alloy in which the nickel isin a proportion of approximately 42% of the alloy, whereby said switchis operated by the dierential expansion and contraction of said soleplate .and actuator.

6. 'I'he structure defined in claim 5, in which said actuator is in theform of a bar incorporated in said sole plate.

7. I'he structure dened in claim 5, in which said switch actuator is mthe :om of a bar m- 25 corporated in said sole plate adjacent thelongitudinal center thereof, land in1whicl1 said actuator is connectedat one en d to said switch and at its other end to the sole plate.

MAURICE H.. GRAHAM;

